DESCRIPTION: (Applicant's Abstract) Slowing aqueous humor secretion is a mainstay of glaucoma therapy. Our goal is to develop a better understanding of cellular mechanisms which regulate secretion. We know secretion is driven by the ion gradients set up by Na,K-ATPase which is most abundant at the basolateral surface of the nonpigmented ciliary epithelium (NPE). Here, we develop and test ideas that function of Na,K-ATPase and other NPE transport proteins can be modulated by changes in cytoplasmic pH (pHi). We have evidence that carbonic anhydrase inhibitors (CAIs) acidify the NPE cell and we hypothesize this could slow aqueous secretion in part because the pH change leads either directly or indirectly to Na,K-ATPase inhibition. In this application, we propose a 5 yr study to examine how ion transport mechanisms in the NPE are set up to respond to pHi changes with the idea in mind that aqueous secretion might be altered in the future by drugs targetted to interfere with cell pHi regulation. The plan comprises three aims. Aim I is to examine mechanisms by which cytoplasmic acidification could trigger inhibition of Na,K-ATPase in the NPE. Aim II is to test the hypothesis that mechanisms which control cytoplasmic sodium in the NPE are sensitive to selective carbonic anhydrase IV inhibition. Aim III is to examine modulation of H+-ATPase function by second messenger pathways. The studies will be conducted with cultured rabbit NPE and freshly isolated rabbit and porcine NPE. Cytoplasmic pH, calcium and sodium concentrations will be determined using fluorescent dyes. Measurements of ouabain-sensitive 86Rb uptake and ATP hydrolysis will be conducted to determine sodium pump (Na,K-ATPase) activity.